This invention relates to a device for the control of the flow of writing means to a writing mechanism of a mechanical writer utilizing a source of compressed air acting upon the fluid surface of the reservoir for the writing means.
Devices of the aforementioned kind serve to provide a sufficient supply for writing means at the beginning of the writing act and to assure the feed of writing means during the whole writing act in which case frequently also a regulation of the feed of writing means is provided dependent on the writing speed. Such devices also assure that at the end of the writing process the feed of writing fluid be stopped dependably, thus preventing the creation of droplets at the writing device, consisting for instance of a capillary-writer.
Most devices of the kind mentioned provide besides a source of compressed air also a source of suction and a regulating device operating so that pressure acts upon the writing fluid during the writing action and at the end of the writing action, the surface of the writing means or the efflux area of the writing device are connected to a source of suction. These known devices for the regulation of the writing means feed are therefore built expensively, are difficult to build and susceptible to interruptions.
Accordingly, an object of the present invention is to overcome the aforementioned disadvantages of known prior art devices and to provide a device for the regulation of the supply of writing means which utilizes relatively low cost elements of construction and which therefore can be built at an advantageous reduced cost but which, on the other hand, assures reliable regulation of the writing means feed at high safety of running and at minimal down-time due to repairs.
The aforementioned object is achieved by providing a device of the aforementioned kind with a valve adjustable relative to the working condition of the writing device, such valve being located between the source of compressed air and the container for the supply of writing means, and by also providing an escape valve which automatically regulates depending on the pressure of the writing means and which is located between the container for the supply of writing means and the writing device.
This arrangement according to the present invention provides in a simple manner for furnishing writing means immediately at the start of the writing process, in other words, when one working condition changes to another one, by exerting through the valve located between the source of compressed air and the container of supply for the writing means and which valve opens simultaneously therewith, a pressure which propagates within the writing means and which automatically opens an efflux valve. At the end of the writing act, the valve arranged between the source of compressed air and the supply container closes and, due to the thereby reduced pressure, the efflux valve also closes so that the feed of writing fluid to the writing device is interrupted. This arrangement is effective with great safety of operation at a comparably low expense of manufacture.
A particular advantage of the invention is encompassed in one embodiment where an electro-mechanical three-way valve or a high speed venting or deaeration valve, preferably is provided for venting or deaerating between the source of pressure and the supply container for the writing means. Such a valve has two switching or operating positions, in one of which the source of compressed air and the container for the means of writing supply are connected and the exhaust or vent is closed and in the other, the conduit to the source of compressed air is interrupted and the supply container is connected or vented to the atmosphere, thus depressurizing it.
When writing begins the three-way valve is brought to the first position and at the end of the writing, the valve is in the second position. Such rapid vent valves need venting conduits having much larger cross sections than the rest of the conduits so that the pressure drop occurs very fast and with a high speed of flow which will cause a reduction of the static pressure in the vented conduit down to a certain amount below the exterior pressure. That produced pressure, although comparatively small, suffices to act upon the writing means across the supply container for the writing means to force the retraction of the writing means column within the writing device at the moment of the ending of the writing action and thereby guarantees the prevention of a droplet formation.
In this arrangement the escape valve is preferably not actuated by a spring but is brought into position of closure by the reduced or under pressure and the escape valve is held there by the influence of a resistive or frictional force until sufficient writing means pressure actuates its opening. The present invention is effective to obtain its objective by applying negative pressure to the writing device at the end of the writing act without the addition of a special device for the needed regulation and production of under pressure.
In a further embodiment of the invention there may be provided alternatively to the aforedescribed arrangement, an electro-mechanically actuated choke valve located between the source of compressed air and the writing means supply container and also a venting valve actuated by a spring in the direction of closure, where the movable valve body of the venting valve is guided with a close fitting within its chamber at least along part of its stroke.
The valve disposed after the source of compressed air is in this case a simple stop valve, in other words, it is opened at the beginning of the writing act so that the source of compressed air is connected to the supply container for the writing means and closed at the end of the writing act. The spring actuated vent valve also opens against the spring force when the pressure of the writing means mounts while the stop valve is open and allows the writing means to flow out. When the stop valve is shut off interrupting the pressure upon the writing means thereby, the spring of the vent valve forces the valve body back into the closed position, at which time a suction is created upon the writing means column remaining between the vent valve and the exit of the writing device because the valve chamber of the valve body is provided with a close fit. This arrangement also does not require any additional devices for providing under pressure.
Advantageously, the vent valve is arranged directly at or close to the writing device. This results in a maximum efficiency of the valve. The simple construction of the valve permits such a liqht weight construction that it only increases the inertia of the writing device so little that it does not lower its mobility.
The present invention also encompasses the provision of an adjustable throttle-valve between the source of the compressed air and the writing device. Such a throttle-valve is capable of regulating the pressure exerted upon the writing means and thus also the amount of writing means flowing out. In the simplest case the regulation of the throttle-valve relative to the expected speed of writing may be effected manually.
In a further embodiment of the invention an electro-mechanically adjustable throttle-valve is provided and also an adjustment device for the adjusting of the throttle-valve as a function of the particular speed of writing. The adjustment device may for instance regulate the throttle-valve as a function of the rate of rotation of the servomotors which actuate the relative motion between the writing plane and writing device. In that way a constant thickness of lines is assured during the whole writing process.
Finally, there may be provided an electro-mechanical device for lifting and positioning the writing device and an electrical coupling for actuation simultaneously with the valve between the source of compressed air and the writing device. That means that the same switching act which for instance actuates the positioning of the writing device at the start of the writing act also opens the valve between the source of compressed air and the supply container. Conversely, this valve is closed when the writing device is lifted off the writing plane.
Other features which are considered characteristic of the invention are set forth in the appended claims.
Although the invention is illustrated and described in relationship to specific embodiments, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.